1. Field of the Invention
The present invention relates to apparatus for use in machining an annular groove in a wall.
2. Description of the Prior Art
There are a large number of pressure vessels presently in use, having walls of steel of substantial thickness. These pressure vessels are used in both steam generating plants and nuclear power plants, and are provided with three-inch thick walls in order to withstand the internal pressures, which are often in the range of 1,100-1,200 pounds per square inch.
It is often necessary to penetrate the shell or wall of such vessels, providing an opening so as to allow inspection of elements within the vessel. Following the penetration of the vessel wall by the making of an opening therein, the opening must be closed, and this is accomplished by providing a plate which is secured over the opening which has been made. It is necessary that a suitable gasket be provided between the plate and the vessel wall, and it has been found to be necessary to provide an annular groove about the opening, in which to position and seat the gasket. The machining of the gasket seat groove has presented a considerable problem, heretofore.
There was used in the providing of the gasket seat groove of annular configuration a tool having a bit, which was rotated about an axis. The bit was rotated by a boring head, driven by an electric motor. In order to stabilize the apparatus, and to provide against undesired movement of the bit, it was conventional to use a large mass, such as a very large motor. The motor was provided not only to rotate the input shaft of the boring head which carried the bit, but was made of extremely large size in order to provide a mass to stabilize the bit. Heretofore, the equipment provided in order to stabilize the bit, for forming the gasket seat groove, totaled as much as 6,000 pounds. Hence, the prior art constructions were cumbersome, heavy and expensive.